Macromolecular polymer polyethylenimine (PEI) modified by many luminescent lanthanide complexes was prepared and purified. The spectral properties and lifetime of this fluorescence probe were measured. The mean number of lanthanide complexes per PEI molecule was measured and calculated. The fluorescent intensity of a macromolecule modified with lanthanide complexes is 6-fold as high as that of a lanthanide complex molecule.